JPH0843827A - Liquid crystal element and its production - Google Patents

Abstract

PURPOSE:To make it possible to greatly improve the performance of a liquid crystal element by enabling selection in such a manner that only the C2 structures or C1 structures are formed by controlling the number of surface ruggedness of the height >=5nm of oriented films and surely eliminating the zigzag defects by mingling of both structures. CONSTITUTION:This liquid crystal element is formed by respectively disposing electrodes (for example, transparent electrodes 2a, 2b of ITO) and the liquid crystal oriented films on the respective opposite surfaces of plural base bodies (for example, transparent substrates 1a, 1b of glass, etc.) facing each other and arranging liquid crystals (more particularly ferroelectric liquid crystals: (FLC) 5 between the plural base bodies. The liquid crystal oriented films 13a, 13b consist of a high-polymer compd. (for example, polyimide) and the ruggedness of the height >=5nm exists at <2.5X10<6> pieces/mm<2> or >=2X10<7> pieces/mm<2> on their surfaces.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides an electrode and a liquid crystal alignment film on each facing surface of a plurality of facing substrates.
Regarding a liquid crystal element in which liquid crystal is arranged between the plurality of substrates and a manufacturing method thereof, in particular, a pair of insulating substrates provided with a transparent electrode and a liquid crystal alignment film respectively in this order are arranged facing each other with a predetermined gap, The present invention relates to a liquid crystal display device in which a ferroelectric liquid crystal is filled in the gap and a manufacturing method thereof.

[0002]

2. Description of the Related Art A ferroelectric liquid crystal display element (FLC display) has a structure as schematically shown in FIG. That is, on a transparent substrate 1a such as glass, I
A transparent electrode layer 2a such as TO (indium tin oxide: conductive oxide in which tin is doped), and a laminate A in which a polyimide film 3a as a liquid crystal alignment film is sequentially laminated; similarly, glass or the like A transparent electrode layer 2b, for example, a laminated body B in which a polyimide layer 3b is sequentially laminated on the transparent substrate 1b, is arranged so that the liquid crystal alignment films, for example, the polyimide layers 3a and 3b face each other. A liquid crystal cell is formed by sandwiching a spacer (not shown) for realizing the cell gap, and the ferroelectric liquid crystal 5 is injected into the cell gap.

In this FLC display, liquid crystal alignment films 3a and 3b for aligning liquid crystals are formed. Liquid crystal molecules are prepared by rubbing a polymer coated on a pair of opposed glass substrates 1a and 1b in the arrow direction in the figure. In general, when the surface alignment is caused, the layer structure of the liquid crystal is inclined in a V shape.

However, there are two inclination directions, and a C ₂ structure bent in the rubbing direction and a C ₁ structure bent in the opposite direction are mixed. When the two layered structures C ₁ and C _{2 in} the tilt direction are present at the same time, at a place where the layered structures tilted in different directions are in contact with each other, as shown in FIG. A zigzag defect 16 occurs, which deteriorates the quality of the display.

Such a mixture of C ₁ and C ₂ structures and a zigzag defect resulting therefrom are peculiar to a liquid crystal alignment film made of a polymer, and other known liquid crystal alignment films of SiO oblique vapor deposition film (SiO In this case, only the C ₁ structure occurs.)
Not seen in. In order to eliminate the above-mentioned zigzag defects when a polymer liquid crystal alignment film is formed, an alignment film with a high pretilt angle is effective, but generally only a C ₁ structure can be formed.

[0006] only be C ₁ structure, it is possible to eliminate the zigzag defects mentioned above. However, since the C ₁ structure has a poorer contrast than the C ₂ structure, if only the C ₁ structure can be formed, there is a limit in improving the performance of the display. In addition, up to now, no method has been known for stably eliminating the zigzag defect peculiar to the ferroelectric liquid crystal.

[0007]

The object of the present invention is to prevent a zigzag defect when a polymer is used as a liquid crystal alignment film and to reproduce a layer structure of liquid crystal into a specific one (particularly C ₂ structure). It is to provide a selectable liquid crystal element and a manufacturing method thereof.

[0008]

As a result of intensive studies on the above-mentioned zigzag defect, the present inventor has found that the liquid crystal layer structure has a specific identical structure (C ₂ structure or C ₁ structure, especially C ₂ structure). ) To prevent zigzag defects,
The present invention has arrived at the present invention to prevent the zigzag defect from being eliminated surely by defining unevenness (that is, surface roughness) on the liquid crystal side surface of the polymer liquid crystal alignment film.

That is, according to the present invention, an electrode (for example, a transparent electrode of ITO) and a liquid crystal alignment film are provided on respective facing surfaces of a plurality of substrates (for example, a transparent substrate such as glass) facing each other, and the plurality of substrates are provided. In a liquid crystal element in which a liquid crystal (particularly, ferroelectric liquid crystal: FLC) is arranged between substrates, the liquid crystal alignment film is made of a polymer compound (for example, polyimide), and the surface has irregularities with a height of 5 nm or more. Is 2.5 × 10 ⁶
The present invention relates to a liquid crystal element characterized in that the number of pieces / mm ² or less or 2 × 10 ⁷ pieces / mm ² or more is present.

The present inventor has found that the liquid crystal side of the polymer liquid crystal alignment film is
Controls unevenness with a height of 5 nm or more on the surface,
 2.5 x 10⁶Pieces / mm²Below (especially 1 x 10⁶Pieces / mm²Below) and special
When determined, the layer structure of the liquid crystal is C₂Structure only
And again, 2 × 10⁷Pieces / mm²Above (especially 2 × 10⁸Pieces / mm²
When the above is specified, the layer structure of the liquid crystal is C above. ₁
It was found that there is only the structure. Based on this, the orientation
By controlling the number of surface irregularities with a film height of 5 nm or more, C₂
Structure only or C₁With the choice that only the structure is formed
To ensure that there is no zigzag defect due to the mixture of both structures.
However, the performance of the liquid crystal element can be greatly improved.

In selectively forming either the C ₂ structure or the C ₁ structure as described above, the number of surface irregularities having a height of 5 nm or more has a difference of at least one digit or more between the two structures. It is indispensable that the above-mentioned number range is satisfied. This is the condition that was first discovered by the present inventor as a result of various studies to be described later, and cannot be predicted from previous studies on the liquid crystal alignment film.

In particular, it is desirable that only the C ₂ structure is used because the contrast can be improved when the liquid crystal element is used as a display.

The above-mentioned control of the number of surface irregularities can be achieved by subjecting the polymer liquid crystal alignment film to rubbing and then surface treatment. Regarding this rubbing, the layer structure of the liquid crystal exhibits a chevron structure bent in the rubbing direction of the liquid crystal alignment film (in the case of C ₂ structure) or in the opposite direction (in the case of C ₁ structure).

In the liquid crystal element according to the present invention, a transparent electrode for displaying information and a liquid crystal alignment film are formed in this order on the opposing surfaces of a pair of insulating substrates, at least one of which is optically transparent. With the liquid crystal alignment film inside,
It is desirable that the pair of insulating substrates be combined with a gap therebetween and that the gap be filled with a ferroelectric liquid crystal to form a liquid crystal display element.

In manufacturing the liquid crystal device according to the present invention, in particular, in order to control the surface unevenness of the polymer liquid crystal alignment film as described above, the polymer liquid crystal alignment film is rubbed and then heat-treated under a predetermined condition, It is desirable to control unevenness having a height of 5 nm or more on the surface of the liquid crystal alignment film as described above.

That is, particularly in the manufacture of a ferroelectric liquid crystal display device, a polymer alignment film is applied on a substrate, baked, and then rubbed in a certain direction, and then the alignment film is heat-treated under certain conditions. Controls the density of the fine surface irregularities formed on the alignment film, and as a result, 100%
It is possible to eliminate the zigzag defect peculiar to the ferroelectric liquid crystal by forming the C ₂ orientation or the C ₁ orientation.

As such heat treatment conditions, firing at 130 ° C. or higher or 70 ° C. or lower is desirable. That is, it was found that firing at 130 ° C. or higher (particularly 150 ° C. or higher) produces only the C ₂ structure, and baking at 70 ° C. or lower (particularly 50 ° C. or lower) produces only the C ₁ structure.

This baking facilitates the movement of polymer molecules in the liquid crystal alignment film, and accordingly, fine projections or depressions formed on the surface of the polymer liquid crystal alignment film after rubbing are pulled in accordance with the movement of the polymer molecules ( Surface transition occurs). In this case, the firing temperature is 130 ℃
When higher than the above, the height becomes low or disappears on the polymer surface for a considerable number of convex portions or concave portions on the surface, and the surface becomes flat, and conversely, the firing temperature is 70 ° C. When it is as low as or less, it is considered that the height does not decrease so much or the number of disappeared particles decreases.

[0019]

Embodiments of the present invention will be described below.

First, for comparison, a SiO oblique vapor deposition film was formed under the following conditions on a glass substrate provided with an ITO transparent electrode, and the two substrates were made of UV resin so that their vapor deposition directions were antiparallel to each other. Then, a 1.6 μm gap was formed between the substrates, and a ferroelectric liquid crystal CS-1014 (manufactured by Chisso Corporation) was injected at 110 ° C. between them to cool at a constant rate to prepare a cell.

Deposition conditions: degree of vacuum <7 × 10 ^-6 Torr deposition angle 85 ° deposition rate 5Å / sec substrate temperature 170 ° C.

The cells thus produced showed a uniform C ₁ orientation without zigzag defects. Then, the deposited film is SE
Observed at M. A column structure with a height of 400Å (40 nm) is 1 × 10 ⁸ /
mm ^{2 was} observed.

Next, to describe an embodiment of the present invention, FIGS. 3 and 4 show the texture of a ferroelectric liquid crystal cell using a polyimide rubbing film. The alignment film and liquid crystal used were as follows.

Polyimide alignment film: Product name LQ-1800 (manufactured by Hitachi Chemical Co., Ltd.) Concentration 4% Coating condition 1000 rpm, 10 sec 3000 rpm, 30 sec Firing condition 180 ° C. Rubbing density 80 Liquid crystal: CS-1014 (manufactured by Chisso Corporation)

A cell for examining the alignment state of liquid crystal was prepared as follows. A polyimide film was formed by spin coating on a glass substrate provided with an ITO transparent electrode, and this film was baked under the above conditions and then rubbed. At the time of manufacturing the cell, two glass substrates were adhered with a UV resin so that the rubbing directions were parallel to each other.

Before the cell was manufactured in this way, the polyimide alignment film was rubbed and then fired as follows.

That is, the substrate having the rubbed polyimide alignment film was heated in a clean oven for a predetermined time (2 hours). As the temperature condition, each measurement point was from room temperature to 180 ° C. as shown in FIG.

FIG. 2 shows the density of the unevenness having a height of 5 nm or more existing on the surface of the polyimide alignment film after firing, depending on the firing temperature.

From the results shown in FIGS. 1 and 2, it can be seen that the layer structure and the uneven density of the liquid crystal change greatly depending on the firing temperature.

That is, according to FIG. 1, in a cell using an alignment film which is baked after rubbing, the ratio of C ₁ alignment and C ₂ alignment as the alignment state of liquid crystal molecules: C ₂ / C
_{As for No. 1} , it can be seen that if the firing temperature is high, the C ₂ orientation increases, and at 130 ° C or higher (particularly 150 ° C or higher), the C ₂ structure is almost completely formed. On the other hand, if the firing temperature is lower than this, the C ₂ structure and the C ₁ structure coexist, and the temperature is 70 ° C or less (especially
It can also be seen that at 50 ° C. or less), only the C ₁ structure is almost completely formed.

Further, according to FIG. 2, the surface shape of the alignment film when the heat treatment is applied to the alignment film after rubbing is observed by an AFM (atomic force microscope). Fluctuates greatly depending on the firing temperature, and the uneven density greatly decreases at 130 ° C or higher (particularly 150 ° C or higher).
It can be seen that the uneven density sharply increases at 70 ° C or lower (particularly 50 ° C or lower). These changes correspond well with the results shown in Fig. 1, and almost 100% of the C ₂ structure has a very small unevenness density (corresponding to 2.5 × 10 ⁶ pieces / mm ² or less in particular).
It can be seen that almost 100% of C ₁ structures appear when the uneven density is quite large (especially when the number corresponds to 2 × 10 ⁷ pieces / mm ² or more).

As described above, by controlling the firing temperature of the polyimide alignment film after rubbing, it is possible to select the layer structure of the liquid crystal to have only the C ₂ structure or the C ₁ structure.

FIG. 3 and FIG. 4 show states of the polyimide alignment film obtained at each of the above firing temperatures as observed by SEM.
According to this, a C ₁ structure is observed up to 100 ° C.
When the temperature exceeds 30 ° C, the C ₂ structure remarkably appears in the C ₁ structure,
It can be seen that when the temperature reaches 150 ° C., only the C ₂ structure is formed (especially when the cell is off).

5 and 6 show AFM images of the polyimide alignment film obtained at each firing temperature. According to this, in addition to the formation of grooves parallel to the rubbing direction in the rubbed polyimide film, there are fine surface irregularities, and the surface of the film is changed depending on the baking temperature of the alignment film after rubbing. The shape changes as follows. 1. The groove in the rubbing direction hardly changes. 2. The higher the firing temperature is, the smaller the number of fine irregularities becomes, and the C ₂ structure is likely to occur.

From these observation results, it is possible to reproducibly control surface irregularities having a height of 5 nm or more by the firing temperature. In addition, in FIGS. 5 and 6, graduations are provided at intervals of 500 nm, and the maximum height from the sample bottom surface to the tip of the convex portion of the unevenness in FIG. 5 is 20 nm.

FIG. 7 shows a display screen of a liquid crystal of C ₂ structure only according to the present invention, but it is clear that there are no zigzag defects.

In the above C ₁ orientation (structure), the V-shaped layer structure of the liquid crystal is tilted in the direction opposite to the rubbing direction, and the C ₂ orientation (structure) is in the V shape. Although the layered structure is inclined in the rubbing direction, it is preferable that the display has a C ₂ structure as shown in FIG. 8 because the contrast is improved. The contrast ratio was defined as follows. Contrast ratio (CR): C.R. R. = Light state transmittance / Dark state transmittance

FIG. 9 shows a specific example of the FLC display according to the present invention. That is, the glass substrate 1 having the ITO transparent electrodes 2a and 2b and the polyimide alignment films 13a and 13b.
A liquid crystal cell is constituted by sandwiching a substance having optical bistability, particularly a ferroelectric liquid crystal 5 between a and 1b (4 in the drawing is a spacer and 6 is a sealant).

As the transparent electrodes, there are N groups of 2b parallel to the X direction as scanning electrodes on the substrate 1b, and M groups of 2a parallel to the Y direction as data electrodes on the substrate 1a. Then, an electric signal for selecting display of a pixel is applied to the transparent electrode 2b parallel to the Y direction, and the content of information to be displayed, white or black, or an intermediate gradation is applied to the transparent electrode 2a parallel to the X direction. Apply an electrical signal to display
Multiplex drive by matrix method.

A display element using TN (twisted nematic) liquid crystal as the liquid crystal can exhibit a certain gradation by being driven by an active matrix system such as a TFT (thin film transistor), but the surface is stabilized. Bistable ferroelectric liquid crystal (FLC)
The display element using the crystal) 5 does not require an active matrix such as a TFT, and has a possibility of realizing a low-cost and large-area display element. Moreover, the FLC display has features such as high-speed response (a 1000 times faster response than the conventional nematic liquid crystal display), less viewing angle dependence, and image memory.

Although the present invention has been described with reference to the embodiments, the above-described embodiments can be further modified based on the technical idea of the present invention.

For example, the number or density of the surface irregularities of the alignment film described above (this can be controlled by the firing temperature,
It also changes with the firing time. ) May be variously changed.

Further, as the kind of liquid crystal, a composition containing Chisso Corporation, Merck Corporation, BDH, or any other known ferroelectric liquid crystal compound or a composition containing a non-chiral liquid crystal can be used. There is no such restriction, and there is no need for restriction of the phase series, and what is necessary is to take a chiral smectic liquid crystal phase in the operating temperature range.

The material, structure, shape, and assembling method of each component of the liquid crystal element may be variously changed, and other polymers such as polyvinyl alcohol and polyoxymethylene can be used for the liquid crystal alignment film. The film method and the rubbing method can be variously performed as well known.

Although the liquid crystal element suitable for the display element has been described in the above embodiments, the present invention is not limited to the display element, and the liquid crystal element is not limited to the filter, the shutter, the display screen of the OA equipment, the screen, or the wobbling. The present invention can also be applied to a phase control element or the like for use in a computer. Any of these,
With the polymer liquid crystal alignment film described above, it is possible to obtain unprecedented performance in terms of transmittance or contrast ratio.

[0046]

As described above, according to the present invention, an electrode (for example, an ITO transparent electrode) and a liquid crystal alignment film are provided on each of opposing surfaces of a plurality of opposed substrates (for example, transparent substrates such as glass). , A liquid crystal (in particular,
In a liquid crystal device in which a ferroelectric liquid crystal: FLC) is arranged, the liquid crystal alignment film is made of a polymer compound (for example, polyimide), and the surface has irregularities with a height of 5 nm or more.
Since 2.5 × 10 ⁶ pieces / mm ² or less or 2 × 10 ⁷ pieces / mm ² or more are present, only the C ₂ structure or only the C ₁ structure can be controlled by controlling the number of surface irregularities with the height of the alignment film of 5 nm or more. It can be selected to be formed, and zigzag defects due to the mixture of these two structures can be surely eliminated, and the performance of the liquid crystal element can be greatly improved.

[Brief description of drawings]

FIG. 1 is a graph showing a change in a liquid crystal layer structure depending on a firing temperature of a polymer liquid crystal alignment film of a liquid crystal display device.

FIG. 2 is a graph showing a change in surface unevenness density of the liquid crystal alignment film according to the same baking temperature.

FIG. 3 is a sketch of an SEM photograph showing the structural change of the liquid crystal alignment film depending on the firing temperature.

FIG. 4 is a sketch similar to FIG.

FIG. 5 is a sketch of an AFM image showing changes in the surface state of the liquid crystal alignment film depending on the firing temperature.

FIG. 6 is a sketch similar to FIG.

FIG. 7 is a sketch showing a state of a display screen of a liquid crystal display device according to the present invention.

FIG. 8 is a graph showing a change in contrast ratio according to a liquid crystal layer structure in a liquid crystal display device.

FIG. 9 is a schematic plan view and a sectional view of the liquid crystal display device.

FIG. 10 is an enlarged cross-sectional view of a main part of a conventional liquid crystal display element.

FIG. 11 is a sketch showing a state of a display screen of the liquid crystal display device.

[Explanation of symbols]

1a, 1b ... Substrate 2a, 2b ... Transparent electrode layer 3a, 3b, 13a, 13b ... Polyimide liquid crystal alignment film 4 ... Spacer 5 ... Liquid crystal 6 ... Sealing agent 16 ... Zigzag defects C ₁ , C ₂ ... Layer structure of liquid crystal

Claims (6)

[Claims] 1. In a liquid crystal device in which an electrode and a liquid crystal alignment film are respectively provided on respective facing surfaces of a plurality of bases facing each other, and a liquid crystal is arranged between the plurality of bases, the liquid crystal alignment film is a polymer compound. And has a height of 5 nm on its surface
The above unevenness is 2.5 × 10 ⁶ pieces / mm ² or less or 2 × 10 ⁷ pieces / mm ²
A liquid crystal element having the above properties. 2. The liquid crystal device according to claim 1, wherein the liquid crystal alignment film is subjected to surface treatment after being rubbed. 3. The liquid crystal device according to claim 2, wherein the layer structure of the liquid crystal has a chevron structure bent in the rubbing direction of the liquid crystal alignment film or in the opposite direction. 4. A transparent electrode for displaying information and a liquid crystal alignment film are formed in this order on opposite surfaces of a pair of insulating substrates, at least one of which is optically transparent, and these transparent electrode and liquid crystal alignment film are provided inside. 2. A pair of insulating substrates are assembled together with a gap therebetween, and a ferroelectric liquid crystal is filled in the gap to form a liquid crystal display element.
3. The liquid crystal device according to any one of items 3 to 3. 5. When manufacturing the liquid crystal element according to any one of claims 1 to 4, after rubbing the liquid crystal alignment film, heat treatment is performed under a predetermined condition to remove irregularities on the surface of the liquid crystal alignment film. A method for manufacturing a liquid crystal element, comprising controlling the unevenness according to claim 1. 6. The manufacturing method according to claim 5, wherein the liquid crystal alignment film is heat-treated at 130 ° C. or higher or 70 ° C. or lower.